Can you draw in 3d from orthografic projections?
All you need to do is switch the view in which you want to draw, so that the strokes are aligned in a different axis.

Blender will not magically merge shapes, though.
But you can edit your objects just like any other object in 3D to get whatever shape and plane you want.

Note that you can also set the grease pencil to draw at different planes, determined by the 3d cursor. That would allow you to draw from the same view, but at different depths.
See: Align Grease Pencil with Camera Angle